The use of a cyclone, or multiple cyclones connected in parallel or series, is known to be advantageous in the separation of particulate matter from a fluid stream. Currently, many vacuum cleaners, which are sold for residential applications, utilize at least one cyclone as part of the air filtration mechanism.
U.S. Pat. No. 4,826,515 (Dyson) discloses a cyclonic vacuum cleaner having two cyclonic stages, namely a first stage for separating larger particulate matter from an air stream and a second stage for separating finer particulate matter from the same air stream. Each cyclonic stage comprised a single cyclone wherein separated particulate matter was collected in the bottom of the cyclones. Vacuum cleaners, which use a cyclonic cleaning stage comprising a plurality of cyclones in parallel, are also known.
Typically, vacuum cleaners also have one or more filters positioned downstream from the cyclone or cyclones and upstream from the suction motor. In addition, a filter, such as a HEPA filter, may be positioned downstream of the suction motor.